Dvortsov I A, Lunina N A, Zverlov V V, Velikodvorskaia G A
Mol Biol (Mosk). 2012 Nov-Dec;46(6):915-21.
At the C-terminus of multimodular laminarinase Lic16A Clostridium thermocellum four carbohydrate-binding modules (CBM), belonging to family 4, were found. The isolated CBM - CBM4_1, CBM4_2, CBM4_3, CBM4_4 and the tandem CBM4_(1-4) were obtained. None of the recombinant proteins did have the affinity to soluble beta-1,3-1,4-glucans--laminarin and lihenan--the main specific substrates of Licl6A. All modules, except CBM4_4, had the ability to bind bacterial crystalline cellulose, that was atypical for the family 4 CBMs. We found that all CBMs 4 of Licl6A had affinity for xylan, chitin, beta-glucan from yeast cell wall and Avicel, while CBM4_3 and CBM4_4 had additional affinity to chitosan. The tandem CBM4_(1-4) had the highest affinity to yeast cell wall beta-glucan, avicel and pustulan. The binding constants for these substrates were about 100 times higher than that of the individual modules, suggesting a synergy in the process of absorption to these polysaccharides. This finding helps to explain the evolutionary process of CBM multiplication.
在嗜热栖热菌多模块海带多糖酶Lic16A的C末端发现了4个属于第4家族的碳水化合物结合模块（CBM）。获得了分离的CBM——CBM4_1、CBM4_2、CBM4_3、CBM4_4以及串联的CBM4_(1-4)。这些重组蛋白均对Lic16A的主要特异性底物——可溶性β-1,3-1,4-葡聚糖（海带多糖和地衣多糖）没有亲和力。除CBM4_4外，所有模块都有结合细菌结晶纤维素的能力，这对第4家族的CBM来说是不典型的。我们发现Lic16A的所有CBM4都对木聚糖、几丁质、酵母细胞壁β-葡聚糖和微晶纤维素有亲和力，而CBM4_3和CBM4_4对壳聚糖还有额外的亲和力。串联的CBM4_(1-4)对酵母细胞壁β-葡聚糖、微晶纤维素和石耳多糖的亲和力最高。这些底物的结合常数比单个模块的结合常数高约100倍，这表明在对这些多糖的吸附过程中存在协同作用。这一发现有助于解释CBM倍增的进化过程。
